In the 1980s a new technology was perfected that would allow weather radars to not only pinpoint the location and intensity of precipitation, but to also peer inside clouds and measure the wind speed and direction. This kind of radar is commonly known as Doppler Radar.

The biggest advantage of Doppler is that it helps us identify which thunderstorms are most likely to produce tornadoes. Such thunderstorms often rotate, and being able to measure wind patterns helps us detect this spin.

At this Franklin Institute web site, I have links to several sources of Doppler radar information:

www.fi.edu/weather/phila.html

You can display the entire country or focus on specific regions. You can look at conventional radar that shows simply where it's raining and how hard, or you can check out the special "velocity" radar mode that shows the winds.